How does a 12AX7 work?

[irish_admiral]

Just a question I was chewing over today... how do 12AX7s work? They're typically in the preamp stage, and add a lot of the distortion in valve amps. So say you have 3 valves instead of 1, you will have a greater range of distortion.

OK, here's the crux though. Imagine an amp had four 12AX7s in the preamp stage... when you adjust the gain dial up does the amp use all four valves to increase the gain? Is the tonal response (ie. increase / decrease in gain, and effect on tone) linearly consistent all the way up the dial?

Would you get a different tonal response from an amp that instead of using all four valves at once, would use one valve up to its maximum capacity (9 o'clock on the dial), then start using the second valve also (12 o'clock), then the 3rd etc.? Would it be possible to do this?

It was just a thought. I know some amps have a similar idea in the output stage insofar as you can 'kick in' extra valves.


Don't tell me the best way, just tell me the cheapest way...

[bclaire]

You'd be better off posting this question on Ted Weber's Amps board:

http://www.webervst.com/vstbbs/bbs.html

You need a more technical answer than you're going to get here.

Billy